Automatic drive control system for a bulldozer

ABSTRACT

An automatic drive control system for a bulldozer comprising a digging start detector for detecting that the bulldozer is in a digging start position, a digging end detector for detecting that the bulldozer is in a digging end position, a driving direction detector for detecting the momentarily varying driving direction of the bulldozer, and a drive controller for shifting a transmission into a forward gear when the digging start detector detects that the bulldozer is presently in the digging start position; shifting the transmission into a reverse gear when the digging end detector detects that the bulldozer is presently in the digging end position; and controlling the bulldozer such that the driving direction detected by the driving direction detector is made coincident with a target driving direction when the bulldozer is moving from the digging start position towards the digging end position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic drive control system forautomatically driving a bulldozer such that the bulldozer moves back andforth predetermined times between a digging start position and a diggingend position.

2. Description of the Prior Art

In most prior art bulldozers, dozing operation is manually performed bythe operator throughout. Specifically, during dozing operation, theoperator lifts and lowers the blade such that the load imposed on theblade during digging and carrying is maintained constant, while avoidingthe occurrence of the running slip (shoe slip) of the vehicle body. Theoperator also operates a steering lever and blade control lever (tiltlever) in order to adjust the driving direction of the bulldozer. Whensuch dozing operation is carried out on the edge of a cliff, theoperator judges where he should drop removed soil by his own eyes orfrom a sign received from an assistant workman.

SUMMARY OF THE INVENTION

To manually perform dozing operation as described above presents thedisadvantage that it involves a number of lifting and loweringoperations so that the operator gets exhausted tremendously even if heis very skillful. Another disadvantage is that when the manual dozingoperation is carried out on the edge of a cliff, there is danger thatthe bulldozer falls off the cliff in the event of operational errors andtherefore the operator has to particularly concentrate his attention onthe work.

The present invention has been made in order to overcome suchdisadvantages and therefore one of the objects of the invention is toprovide an automatic drive control system for a bulldozer that iscapable of automatically determining a digging starting position, adigging end position and a direction in which the bulldozer should bedriven, so that limitative unmanned drive becomes possible.

In accomplishing this and other objects, there has been provided, inaccordance with the present invention, an automatic drive control systemfor a bulldozer which is capable of automatically driving a bulldozersuch that the bulldozer moves back and forth predetermined times betweena digging start position and a digging end position, the automatic drivecontrol system comprising:

(a) digging start detecting means for detecting that the bulldozer is inthe digging start position;

(b) digging end detecting means for detecting that the bulldozer is inthe digging end position;

(c) driving direction detecting means for detecting the momentarilyvarying driving direction of the bulldozer; and

(d) drive controlling means for shifting a transmission into a forwardgear when the digging start detecting means detects that the bulldozeris presently in the digging start position; shifting the transmissioninto a reverse gear when the digging end detecting means detects thatthe bulldozer is presently in the digging end position; and controllingthe bulldozer such that the driving direction detected by the drivingdirection detecting means is made coincident with a target drivingdirection when the bulldozer is moving from the digging start positiontowards the digging end position.

According to the above-described automatic drive control system, afterthe bulldozer has been guided to the digging start position and aninstruction has been released to start digging, the transmission isshifted into a forward gear and the bulldozer is forwardly driventowards the digging end position, whereby the desired dozing operationis automatically carried out. During the forward driving which involvesdozing, the momentarily varying driving direction of the bulldozer isdetected by the driving direction detecting means, and control isperformed such that the detected driving direction is made coincidentwith a target driving direction. When the bulldozer has reached thedigging end position, for example, on the edge of a cliff, thetransmission is shifted into a reverse gear so that the bulldozer isdriven back towards the digging start position. In such a way, thebulldozer moves back and forth predetermined times between the diggingstart position and the digging end position, while its driving directionis being corrected, and thus unmanned dozing operation is carried out ina specified lane. With such a control, fatigue of the operator can bereduced and safety can be ensured even if the dozing operation iscarried out on a cliff.

Preferably, the automatic drive control system further comprises drivingdirection changing means for changing the driving direction of thebulldozer.

Preferably, the automatic drive control system further comprises bladecontrolling means for controlling lifting and lowering of the blade suchthat an actual tractive force exerted on the vehicle body is madecoincident with a set target tractive force while the bulldozer ismoving from the digging start position towards the digging end position.

The digging start detecting means preferably comprises (i) at least onelaser projector installed on the ground and (ii) a laser beam sensorincorporated in the bulldozer for receiving a laser beam directed fromthe laser projector. Alternatively, the digging start detecting meansmay comprise (i) at least one laser beam projecting/receiving deviceinstalled on the ground and (ii) a reflector incorporated in thebulldozer for reflecting a laser beam directed from the laser beamprojecting/receiving device in the same direction. Further, the diggingstart detecting means may be a detector which detects that the bulldozerhas returned to the digging start position, by counting the number ofrevolutions of sprockets for actuating crawler belts, the count beingstarted immediately after the bulldozer has left the digging endposition when the bulldozer moves backwards.

The digging end position may be an edge of a cliff from which removedsoil is to be dropped and the digging end detecting means may bedesigned to detect that the forward end of the bulldozer is on the edgeof a cliff. Concretely, the digging end detecting means may comprise (i)at least one laser projector installed on the ground and (ii) a laserbeam sensor incorporated in the bulldozer for receiving a laser beamdirected from the laser projector. Alternatively, the digging enddetecting means may comprise (i) at least one laser beamprojecting/receiving device installed on the ground and (ii) a reflectorincorporated in the bulldozer for reflecting a laser beam directed fromthe laser beam projecting/receiving device in the same direction.Further, the digging end detecting means may comprise an ultrasonicsonar incorporated in the bulldozer for projecting ultrasonic wavesahead of the vehicle body to detect the presence or absence of theground. In this case, the projecting angle of the ultrasonic sonar ispreferably adjustable. Further, the digging end detecting means maycomprise a load detector for detecting a change in the load imposed onthe blade to estimate the amount of soil present in front of the blade.

In the digging start detecting means and the digging end detectingmeans, the laser projector may be rotatable within a vertical plane andthe laser beam sensor may be arranged such that its longitudinal axis ishorizontally oriented. In these means, the laser beamprojecting/receiving device may be rotatable within a horizontal planeand the reflector may be disposed such that its longitudinal axis isvertically oriented.

The driving direction detecting means may comprise an azimuth sensor fordetecting a direction utilizing earth magnetism. Alternatively, thedriving direction detecting means may comprise (i) at least two laserbeam projecting/receiving devices installed on the ground which arerotatable within a horizontal plane to project laser beamssynchronously, and (ii) a reflector which reflects laser beams directedfrom the laser beam projecting/receiving devices in the same directionand which is provided in the bulldozer such that its longitudinal axisis vertically oriented. Further, the driving direction detecting meansmay comprise (i) at least one laser projector installed on the groundand rotatable within a vertical plane, and (ii) at least two laser beamsensors which are provided in the bulldozer such that their longitudinalaxes are horizontally oriented and which receive a laser beam directedfrom the laser projector. These laser beam sensors detect the relativeangle between the plane of a laser beam directed from the laserprojector and the vehicle body, thereby detecting the driving directionof the bulldozer. Further, the driving direction detecting means maydetect the driving direction of the bulldozer by integrating data from ayaw rate gyro.

The driving direction changing means may be a steering system whichtransmits the power of an engine to the right and left sprockets foractuating the crawler belts with the help of clutches and brakes. Theseclutches and brakes may be independently engaged or disengaged prior toa start of dozing operation to change the driving direction of thebulldozer. Further, the driving direction changing means may tilt theblade laterally during dozing operation to change the driving directionof the bulldozer.

The automatic drive control system of the invention may include remotecontrol means for guiding the bulldozer to the desired digging lane. Theprovision of the remote control means allows the operator to guide thebulldozer from a position remote from the bulldozer so that one operatorcan supervise a plurality of bulldozers.

Other objects of the present invention will become apparent from thedetailed description given hereinafter. However, it should be understoodthat the detailed description and specific examples, while indicatingpreferred embodiments of the invention, are given by way of illustrationonly, since various changes and modifications within the spirit andscope of the invention will become apparent to those skilled in the artfrom this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and accompanying drawings whichare given by way of illustration only, and thus are not limitative ofthe present invention, and wherein:

FIGS. 1 to 12 provide illustrations of preferred embodiments of anautomatic drive control system for a bulldozer according to theinvention;

FIG. 1 is a view of the external appearance of the bulldozer;

FIG. 2 is a skeleton diagram of a power transmission system of thebulldozer;

FIG. 3 is a schematic block diagram of the overall construction of theautomatic drive control system;

FIG. 4 is a detailed view of a blade lift cylinder stroke sensor;

FIG. 5 is a perspective view of the bulldozer as it is in dozingoperation according to a first embodiment;

FIG. 6 is a perspective view of a laser beam sensor;

FIG. 7 is a flow chart of a basic program for the automatic drivecontrol system;

FIG. 8 is a flow chart of a driving direction correction routine;

FIG. 9 is a graph showing a characteristic map of steering instructions;

FIG. 10 is graphs showing patterns of load applied to a blade;

FIG. 11 is a perspective view of a bulldozer as it is in dozingoperation according to a second embodiment; and

FIG. 12 is a perspective view of a reflector according to the secondembodiment.

PREFERRED EMBODIMENTS OF THE INVENTION

With reference to the drawings, preferred embodiments of an automaticdrive control system for a bulldozer according the invention will behereinafter described.

Referring initially to FIG. 1, there is shown the external appearance ofa bulldozer 1. The bulldozer 1 is provided with, on a vehicle body 2thereof, a bonnet 3 for housing an engine (not shown) and an operatorseat 4 for the operator who drives the bulldozer 1. Both sides (i.e.,the right and left sides of the vehicle body 2 when viewing in itsmoving direction) of the vehicle body 2 are provided with crawler belts5 for turning the vehicle body 2 or driving it back and forth. Note thatthe crawler belt 5 on the right side is now shown in the drawing. Thesecrawler belts 5 are independently driven by their respective sprockets 6actuated by driving force transmitted from the engine.

On the right and left sides of the vehicle body 2, there are providedstraight frames 8, 9 for supporting a blade 7 at the forward endsthereof. The base ends of these right and left straight frames 8, 9 arepivotally supported on the vehicle body 2 by means of trunnions 10 insuch a manner that the blade 7 can be lifted or lowered. Note that thetrunnion 10 on the right side is not shown.

Disposed between the blade 7 and the vehicle body 2 are right and leftblade lift cylinders 11 arranged in a pair for lifting or lowering theblade 7. For tilting the blade 7 to the right and left, there areprovided a brace 12 between the blade 7 and the left straight frame 8and a blade tilt cylinder 13 between the blade 7 and the right straightframe 9.

There are provided a steering lever 15, a gear shift lever 16 and a fuelcontrol lever 17 on the left of the operator seat 4 when viewing in themoving direction. On the right of the operator seat 4, there areprovided a blade control lever 18 for lifting and lowering the blade 7and tilting it to the right and left; a first dial switch 19A forsetting an amount of load to be imposed on the blade 7; a second dialswitch 19B for correcting the set amount of load; a lock-up selectorswitch 20 for switching the lock-up mechanism of a torque convertor ONor OFF; and a display unit 21. Disposed on the top of the blade controllever 18 is an operation mode selector button 22 for switching dozingoperation among a manual operation mode, an automatic digging mode andan automatic carrying mode, according to how many times the button 22has been depressed. Although they are not shown in the drawing, a brakepedal and a decelerator pedal are disposed in front of the operator seat4.

Referring to FIG. 2 which shows a power transmission system, rotarydriving force from an engine 23 is transmitted to a torque convertorunit 24 which includes a torque convertor 24a and a lock-up clutch 24b.Then, the rotary driving force is transmitted from the output shaft ofthe torque convertor unit 24 to a transmission 25 whose input shaft iscoupled to the output shaft of the torque convertor unit 24. Thetransmission 25 is, for example, a planetary gear lubricatedmultiple-disc clutch transmission and includes forward and reverseclutches 25a, 25b and first to third clutches 25c to 25e so that therevolution speed of the output shaft of the transmission 25 can beshifted in three ranges in both forward and backward directions. Therotary driving force from the output shaft of the transmission 25 istransmitted to a steering unit 26 which includes a pinion 26a and atransverse shaft 26e on which there are disposed a bevel gear 26b, rightand left steering clutches 26c arranged in a pair, and fight and leftsteering brakes 26d arranged in a pair. Thereafter, the rotary drivingforce is transmitted to right and left final reduction mechanisms 27arranged in a pair so that each of the sprockets 6 for running thecrawler belts 5 (not shown in FIG. 3) is driven.

The clutches 25a to 25e provided in the transmission 25 areindependently controlled by their corresponding electronic modulationvalves 29a to 29e respectively, in response to control signals from atransmission controller 28. Similarly, the right and left steeringclutches 26c and the right and left steering brakes 26d of the steeringunit 26 are independently controlled by their corresponding electronicmodulation valves 31a to 31d respectively, in response to controlsignals from a steering controller 30. Reference numeral 32 denotes anengine revolution sensor for detecting the revolution speed of theengine 23 and reference numeral 33 denotes a torque convertor outputshaft revolution sensor for detecting the revolution speed of the outputshaft of the torque convertor unit 24.

Referring to FIG. 3 which schematically shows the overall constructionof the automatic drive control system for a bulldozer according to oneembodiment of the invention, the following data items are provided overa bus 34 to a microcomputer 35: (i) dial value data from the first dialswitch 19A, regarding a set amount of load to be imposed on the blade 7;(ii) dial value data from the second dial switch 19B, regarding acorrection value for the set amount of load; (iii) button pressing statedata from the operation mode selector button 22, regarding which of themodes (manual operation mode, automatic digging mode, automatic carryingmode for dozing operation) has been selected; (iv) revolution speed datafrom the engine revolution sensor 32, regarding the revolution speed ofthe engine 23; and (v) revolution speed data from the torque convertoroutput shaft revolution sensor 33, regarding the revolution speed of theoutput shaft of the torque convertor unit 24.

The following data items are also provided over the bus 34 to themicrocomputer 35: (i) stroke positional data from fight and left bladelift cylinder stroke sensors 36 which detect the amount of strokes ofthe pair of right and left blade lift cylinders 11 for lifting orlowering the blade 7; (ii) pitch angle data from a pitch angle sensor 37for detecting the momentarily varying pitch angle of the vehicle body 2;(iii) speed range state data from a transmission speed range sensor 38for detecting which of the speed ranges has been selected in thetransmission 25 by operating the gear shift lever 16; (iv) manualoperation state data from a blade operation sensor 39 which detectswhether the blade 7 is being manually operated by the blade controllever 18; (v) LU/TC state data from a torque convertor LU/TC sensor 40which detects the state (locked-up (LU) or torque converting (TC)) ofthe torque convertor, the state being changed by operating the lock-upselector switch 20; (vi) bulldozer positional data from laser beamsensors 41 (41_(S), 41_(E)), regarding the present position of thebulldozer 1, the laser beam sensors 41 receiving laser beams from laserprojectors 57_(S), 57_(E) (to be described later) installed on theground; (vii) yaw angle data from a yaw rate gyro 42 of the opticalfiber type, which measures the yaw angle (yaw angular rate) of thevehicle body 2 relative to a target driving direction; (viii) rollingangle data from a rolling angle sensor 43 which detects the momentarilyvarying rolling angle of the vehicle body 2; and (ix) dial value datafrom a reciprocation frequency setting switch 44 which sets the numberof reciprocating movements to be carried out by the bulldozer 1 in aspecified lane, when the bulldozer 1 is in automatic operation.

The microcomputer 35 is composed of a central processing unit (CPU) 35Afor executing a specified program; a read only memory (ROM) 35B forstoring this program and various maps; a random access memory (RAM) 35Cserving as a working memory necessary for executing the program and asregisters for various data; and a timer 35D for measuring elapsed timefor an event in the program. The program is executed in accordance with(i) the dial value data, regarding a set amount of load to be imposed onthe blade 7; (ii) the dial value data, regarding a correction value forthe set amount of load; (iii) the button pressing state data from theoperation mode selector button 22; (iv) the revolution speed data of theengine 23; (v) the revolution speed data of the output shaft of thetorque convertor unit 24; (vi) the stroke positional data of the rightand left blade lift cylinders 11; (vii) the pitch angle data of thevehicle body 2; (viii) the speed range state data of the transmission25; (ix) the manual operation state data of the blade 7; (x) the LU/TCstate data of the torque convertor; (xi) the bulldozer positional dataof the bulldozer 1; (xii) the yaw angle data of the vehicle body 2relative to a target driving direction; (xiii) the rolling angle data ofthe vehicle body 2; and (xiv) the dial value data regarding the numberof reciprocating movements to be carried out by the bulldozer 1 when thebulldozer 1 is in automatic operation. As a result, data on a liftoperation amount for lifting or lowering the blade 7 is supplied to theblade lift cylinder controller 45, which controls a lift valve actuator46 to actuate the pair of right and left blade lift cylinders 11 basedon the lift operation amount. Also, data on a tilt operation amount fortilting the blade 7 laterally is supplied to a blade tilt cylindercontroller 47, which controls a tilt valve actuator 48 to actuate theblade tilt cylinder 13, based on the tilt operation amount. Further, aswitch-over signal for shifting speed ranges and driving directions(forward and reverse) is sent to the transmission controller 28, whichcontrols a transmission actuator 49 to actuate the forward clutch 25a,the reverse clutch 25b, and the first to third clutches 25c, 25d, 25e. Asignal for operating the steering unit 26 is also supplied to thesteering controller 30, which controls a steering actuator 50 to actuatethe steering clutches 26c and the steering brakes 26d. The display unit21 displays information such as whether the bulldozer 1 is presently inthe manual operation mode, the automatic digging mode or the automaticcarrying mode for dozing operation.

The blade lift cylinder stroke sensors 36 detect, as shown in FIG. 4,the strokes of the blade lift cylinders 11, by measuring the amount ofthe inclination of each of the blade lift cylinders 11. Note that FIG. 4shows, in an enlarged form, the left side of the bulldozer 1 and thefollowing description is based on either of the side. The blade liftcylinder 11 is supported by a disk-shaped cylinder supporting member 52which is so supported as to be freely rotatable in a vertical planerelative to a mounting bracket 51. The bracket 51 is fixedly attached tothe vehicle body 2 of the bulldozer 1. Disposed adjacent to the cylindersupporting member 52 on the vehicle body 2 is a potentiometer 53 whichconstitutes a part of the blade lift cylinder stroke sensor 36. An arm55 is attached to a pivoting shaft 54 of the potentiometer 53 and theforward end of the arm 55 is coupled to the rotating portion of thecylinder supporting member 52 by means of a rod 56. When the blade liftcylinder 11 is operated to rotate from the position indicated by a chainline to the position indicated by a two-dot chain line (see FIG. 4), thearm 55 is pushed by the rod 56 so that the arm 55 pivots in thedirection of arrow P. This pivoting angle is detected by thepotentiometer 53. Since each of the fight and left blade lift cylinders11 has its own blade lift cylinder stroke sensor 36, the differencebetween the pivoting angles of the blade lift cylinders 11 can beobtained by arithmetic operation. With this difference, the tiltingamount of the blade 7 which is tilted by the operation of the blade tiltcylinder 13 can be detected as well.

As shown in FIG. 5, the laser projectors 57_(S), 57_(E) are installed onthe ground in a job site where dozing operation is carried out by thebulldozer 1 of this embodiment. The laser projector 57_(S) is installedat a digging start position S, while the laser projector 57_(E) at adigging end position E (on the edge of a cliff). The respective laserprojecting parts of the projectors 57_(S), 57_(E) can be rotated aroundan horizontal axis (which is parallel with the driving direction(direction A in FIG. 5) of the bulldozer 1) in the direction of arrow B,so that two vertical planes C, D are formed in the working area of thebulldozer 1 by laser beams projected from the laser projectors 57_(S),57_(E). On the bonnet 3 of the bulldozer 1, there are provided laserbeam sensors 41_(B) which are aligned laterally to receive laser beamsfrom the laser projectors 57_(S), 57_(E) (these sensors are not shown inFIG. 1). Each laser beam sensor 41_(B) is hexagonal prismatic and formedby layered light receiving parts. These laser beam sensors 41_(B) aredisposed with their longitudinal axes being parallel with the drivingdirection of the bulldozer 1, so that the sensors 41_(B) intersect thevertical planes C, D formed by the laser beams when the bulldozer 1 isin predetermined positions. The arrow in FIG. 6 represents an incidentlaser beam. Disposed on the ground opposite to the laser projectors57_(S), 57_(E) are laser beam sensors 41_(S), 41_(E). These sensors41_(S), 41_(E) are placed at the substantially same level as the laserbeam sensors 41_(B) provided in the bulldozer 1 and have the samestructure as those of the laser beam sensors 41_(B). The laser beamsensors 41_(S), 41_(E) on the ground are also disposed with theirlongitudinal axes parallel with the driving direction of the bulldozer 1in order to confirm that laser beams are projected from the laserprojectors 57_(S), 57_(E).

With the above-described arrangement, when a laser beam projected fromthe laser projector 57_(S) placed in the digging start position S isreceived by the laser beam sensors 41_(B) provided on the bulldozer 1,it is judged that the bulldozer 1 is in the digging start position S. Onthe other hand, when a laser beam projected from the laser projector57_(E) placed in the digging end position E is received by the laserbeam sensors 41_(B) provided on the bulldozer 1, it is judged that thebulldozer 1 is in the digging end position (on the edge of a cliff) E.

The reason for providing the bulldozer 1 with the two laser beam sensors41_(B) disposed on the right hand and the left hand is that the relativeangle between the vertical plane C formed by a laser beam and thevehicle body 2 is detected to determine the driving direction of thebulldozer 1. Specifically, the right and left laser beam sensors 41_(B)detect the relative angle between the vertical plane C and the vehiclebody 2, for example, in every cycle of the bulldozer 1 (i.e., eachreciprocation), and with the angle thus detected, a reference value forthe yaw rate gyro 42 is set or corrected. This reference value is usedfor obtaining the amount of the deviation of the bulldozer 1 from atarget driving direction.

With reference to the flow chart of FIG. 7 showing a basic program forthe automatic drive control system, the operation of the above describedautomatic drive control system for a bulldozer will be described.

Step 1: Power is loaded to start execution of the specified program andto execute initialization such as clearing of all the data of theregisters in the RAM 35C. Note that the bulldozer 1 has been manuallyguided by the operator to the digging start position S so that it facesin a moving direction for digging. At the digging start position S, theoperator manually sets a dial value corresponding to the amount of loadto be imposed on the blade 7, a speed range for the transmission 25, anda dial value corresponding to the number of reciprocating movements (thenumber of digging cycles)in one lane. Then, the operator releases aninstruction for starting digging.

Step 2: The following data items are read: (i) dial value data from thefirst dial switch 19A, regarding a set amount of load to be imposed onthe blade 7; (ii) dial value data from the second dial switch 19B,regarding a correction value for the set amount of load; (iii) buttonpressing state data from the operation mode selector button 22, (iv)revolution speed data from the engine revolution sensor 32, regardingthe revolution speed of the engine 23; (v) revolution speed data fromthe torque convertor output shaft revolution sensor 33, regarding therevolution speed of the output shaft of the torque convertor unit 24;(vi) stroke positional data from the blade lift cylinder stroke sensors36, regarding the strokes of the pair of right and left blade liftcylinders 11; (vii) pitch angle data from the pitch angle sensor 37,regarding the pitch angle of the vehicle body 2; (viii) speed rangestate data from the transmission speed range sensor 38; (ix) manualoperation state data of the blade 7 from the blade operation sensor 39;(x) LU/TC state data from the torque convertor LU/TC sensor 40; (xi)bulldozer positional data from the laser beam sensors 41 (41_(S),41_(E)), regarding the present position of the bulldozer 1; (xii) yawangle data from the yaw rate gyro 42, regarding the yaw angle of thevehicle body 2 relative to a target driving direction; (xiii) rollingangle data from the rolling angle sensor 43, regarding the rolling angleof the vehicle body 2; and (xiv) dial value data from the reciprocationfrequency setting switch 44, regarding the number of reciprocatingmovements to be carried out by the bulldozer 1, when the bulldozer 1 isin automatic operation.

Step 3 to Step 5: The CPU waits until a digging start instruction hasbeen released and upon release of the instruction, the forward clutch25a of the transmission 25 is engaged. After the engagement, thebulldozer 1 starts forward movement towards the digging end position E.During the forward movement of the bulldozer 1 (more precisely, prior todozing operation), the driving direction of the bulldozer 1 is correctedaccording to a driving direction correction routine to be describedlater (see FIG. 8), so that the bulldozer 1 is controlled to move in astraight direction.

Step 6 to Step 7: The bulldozer 1 carries out dozing until the laserbeam sensors 41_(B) receive a laser beam from the laser projector57_(E), in other words, until the bulldozer 1 has reached the diggingend position (on the edge of a cliff) E. During the dozing operation,the blade lift cylinders 11 are actuated by the blade lift cylindercontroller 45 such that the actual tractive force exerted on the blade 7is coincident with a target tractive force. If the yaw rate gyro 42detects that the bulldozer 1 deviates from the target driving direction,a necessary blade tilt amount is obtained from a characteristic map (notshown) in which blade tilt amounts are plotted against yaw angles, andaccording to the blade tilt amount obtained, the blade tilt cylinder 13is actuated by the blade tilt cylinder controller 47 to correct thedriving direction.

Step 8: After the laser beam sensors 41_(B) have detected that thebulldozer 1 reached the digging end position (on the edge of a cliff) E,the forward clutch 25a of the transmission 25 is disengaged and thereverse clutch 25b is engaged.

Step 9 to Step 10: The bulldozer 1 moves backwards along the specifieddigging lane, with the blade 7 being lifted at a specified level fromthe ground, until the laser beam sensors 41_(B) receive a laser beamfrom the laser projector 57_(S), in other words, until the bulldozer Icomes back to the digging start position S.

Step 11 to Step 12: If the bulldozer 1 has not reciprocated the setnumber of times, the forward and backward movement of the bulldozer 1 inthe same lane is repeated until the set number of reciprocations isreached. If the bulldozer 1 has reciprocated the set number of times,the dozing operation in the lane is completed and the bulldozer 1 isautomatically stopped. When dozing operation in one lane (first lane)has been completed, the bulldozer 1 is manually guided by the operatorto another lane (second lane) which is, for example, adjacent to thefirst lane, and dozing operation is carried out in the second lane inthe same manner as described earlier.

Reference is now made to the flow chart of FIG. 8 for describing thedriving direction correction routine (Step 5) which is performed priorto the start of the above-described dozing operation.

Step 5-1: The deviation amount Δφ of the present driving direction fromthe target driving direction for the bulldozer 1 is obtained byintegrating data from the yaw rate gyro 42.

Step 5-2: Based on the deviation amount Δφ thus obtained, a steeringinstruction is obtained from the steering instruction characteristiccurve map of FIG. 9. The steering instruction obtained is sent to thesteering controller 30, which controls the steering actuator 50according to the steering instruction to actuate the steering clutches26c and the steering brakes 26d, so that the driving direction of thebulldozer 1 is corrected.

Step 5-3: If the deviation amount Δφ is not more than a set value, theflow is terminated. On the other hand, if the deviation amount Δφ ismore than the set value, each step described earlier is repeated.

In the foregoing embodiment, the bulldozer 1 is automatically driven ina preset speed range selected from first to third speeds, but thebulldozer 1 is not necessarily driven in a preset speed range. Forexample, the following way may be taken. A maximum speed range ismanually set by the operator. During automatic dozing operation, thespeed of the bulldozer 1 may be automatically changed up to the setmaximum speed range, according to the detected actual tractive force.During automatic backward movement, the speed is automatically changedup to the set maximum speed range, according to the inclination angle ofthe ground.

In the foregoing embodiment, the bulldozer 1 is guided to a specifiedlane by the manual operation of the operator. However, the operator mayuse a radio controller (remote controller by radio waves) at a pointremote from the bulldozer 1, for guiding the bulldozer 1 to a specifiedlane; for determining the digging start position and the digging endposition; for setting a target tractive force, a maximum speed rangeanti the number of digging cycles; for changing lanes; and forperforming ripper control. The use of a radio controller reduces thetime required for operating one bulldozer, so that one operator cansupervise a plurality of bulldozers 1. This increases the efficiency ofthe dozing operation. In this case, it is preferable that the radiocontroller is equipped with an emergency stop button so that thebulldozer 1 can be stopped in case of emergency by depressing thisemergency stop button by the operator. Further, it is preferable toincorporate a system for dealing with abnormal situations. In the eventthat an abnormal situation arises in the bulldozer 1, for example, whenabnormal water temperature or abnormal oil temperature is detected by avehicle monitor, the system stops the bulldozer 1 after backwardlymoving it to the digging start position and lights a lamp for indicatingthe occurrence of an abnormality.

Although two laser beam sensors 41_(B) arc disposed on the right andleft side of the bonnet 3 in the foregoing embodiment, it is readilyapparent that another laser beam sensor 41_(B) may be provided on thecabin (not shown in FIG. 1). The first and second laser beam sensors41_(B) on the bonnet 3 may be used for detecting a dropping positionfrom which soil will be dropped to start controlling the dropping workof the bulldozer 1, while the third laser beam sensor 41_(B) on thecabin may be used for determining a position from which backwardmovement starts.

In order to make the detection of the dropping position (the edge of acliff) more reliable and to securely prevent the bulldozer 1 fromfalling off the edge of a cliff, a required number of ultrasonic sonarsmay be provided at specified positions of the vehicle body 2. Thesesonars detect the distance to the ground which serves as a reflector,and it can be judged that a place where any of the sonars does not reactis the dropping position. In a preferred embodiment, each side of thevehicle body 2 is provided with an ultrasonic sonar such that the sonarsproject ultrasonic waves diagonally ahead of the vehicle body 2. Wheneither of the ultrasonic sonars does not react, it is judged that thebulldozer 1 is on the edge of a cliff. In this case, the mounting angle(i.e., projecting angle) of each ultrasonic sonar may be adjustable inaccordance with how soil is dropped from the cliff. This ultrasonicsonar may be designed to release an emergency stop instruction when thebulldozer abnormally comes near to another bulldozer. In this way, theultrasonic sonar can be utilized for preventing a bulldozer crush.

The dropping position can be detected by other means than ultrasonicsonars. For example, it may be detected from a change pattern of anactual tractive force exerted on the blade 7. Specifically, thisdetection method is based on the fact that after soil has been droppedfrom a cliff, the load imposed on the blade 7 decreases sharply as shownin FIG. 10. Therefore, it can be judged from such a change in the loadthat the bulldozer 1 is on the edge of a cliff. FIG. 10(a) shows a loadpattern in cases where soil is dropped at one time (one-time dropping).FIG. 10(b) shows a load pattern in cases where some of soil is droppedupon completion of a first forward movement, and then the bulldozer 1moves back once to start a second forward movement and the rest of soilis dropped upon completion of the second forward movement (two-timedropping).

These dropping position detecting means (i.e., ultrasonic sonars and adetector for detecting a load change) are preferably employed asauxiliary means for the detecting means comprised of the laserprojectors and laser beam sensors. The use of a plurality of detectorsensures more reliable detection of the edge of a cliff.

Reference is made to FIG. 11 for describing another embodiment of theposition and direction measuring system for the bulldozer 1.

In this embodiment, the corners of the dozing area of the bulldozer 1are provided with four laser beam projecting/receiving devices 58_(S),58_(E), respectively. Disposed on a cabin 60 of the bulldozer 1 is areflector (corner cube linear array) 59 for reflecting laser beamsdirected from the laser beam projecting/receiving devices 58_(S), 58_(E)in the same direction. The laser projecting part of each of the laserbeam projecting/receiving devices 58_(S), 58_(E) is rotatable around avertical axis in the direction of arrow F, so that a horizontal plane Gis formed in the dozing area of the bulldozer 1 by laser beams projectedfrom the laser beam projecting/receiving devices 58_(S), 58_(E). Thereflector 59 is hexagonal prismatic as shown in FIG. 12 and disposedwith its longitudinal axis being vertically oriented such that thereflector 59 intersects the horizontal plane G. The arrows in FIG. 12represent an incident laser beam and a reflected laser beam,respectively. The long shape of the reflector 59 allows the reflector 59to perform reliable positional detection even if the vehicle body 2 ofthe bulldozer 1 rocks laterally during driving. In this embodiment, datafrom the laser beam projecting/receiving devices 58_(S), 58_(E) is inputto a computer (not shown) installed on the ground.

According to this embodiment, all the laser beam projecting/receivingdevices 58_(S), 58_(E) are rotated synchronously so that the presentposition of the bulldozer 1 can be obtained from the principle of"trigonometrical survey" by the use of the laser beamprojecting/receiving devices 58_(S), 58_(E) located at the two positions(i.e., the digging start position and the digging end position). Bycontinuously tracking the position of the bulldozer 1 with the laserbeam projecting/receiving devices 58_(S), 58_(E), the driving directionand actual vehicle speed of the bulldozer 1 can be obtained througharithmetic operation. Data obtained from the arithmetic operation issent from the computer on the ground to the bulldozer 1 by radiotransmission, and based on the data, the operation of the bulldozer 1 iscontrolled.

The use of the position and direction measuring system of the secondembodiment makes it possible to correct the driving direction withoutthe yaw rate gyro 42 which is used in the first embodiment. It is alsopossible to correct the reference value for the yaw rate gyro 42,according to a driving direction calculated from data sent from thelaser beam projecting/receiving devices 58_(S), 58_(E). Like the firstembodiment, dropping position detecting means may be used together withthe system of the second embodiment. There are advantages in using thedropping position detecting means together with the system of the secondembodiment; for example, the danger of falling off a cliff can benotified to the operator even when manual operation is carried out.Therefore, the system can exert its full efficiencies.

It is to be understood that although four laser beamprojecting/receiving devices 58_(S), 58_(E) arc employed in the secondembodiment for fear that other bulldozers might intercept laser beamswhen a plurality of bulldozers arc operated, two laser beamprojecting/receiving devices are enough to carry out the measurement ofthe position and driving direction of the bulldozer 1.

In addition to the yaw rate gyro 42 and the two laser beamprojecting/receiving devices 58_(S), 58_(E), an azimuth sensor, whichdetects the azimuth of the bulldozer 1 by utilizing earth magnetism, maybe used as the means for detecting the driving direction of thebulldozer 1. However, it should be noted that in the case of utilizingthe azimuth sensor, the bulldozer 1 has to be stopped for a specifiedtime when the driving direction of the bulldozer 1 is sensed by thesensor.

Although a laser beam is used in the foregoing embodiments for detectingthat the bulldozer 1 has returned to the digging start position S, thereturn of the bulldozer 1 may be determined in the following way. Whenthe bulldozer 1 moves backwards, the number of revolutions of thesprockets 6 for actuating the crawler belts is counted immediately afterit has left the digging end position E. From the number of revolutionscounted, the backward moving distance of the bulldozer 1 could beobtained.

In the foregoing embodiment, the bulldozer 1 is automatically driven ina specified lane while changing of lanes is carried out by manualoperation (including radio control). However, changing lanes could becarried out automatically with a digging program for a preset workingarea, the program being preliminarily input in a computer. In this case,unmanned dozing operation can be carried out for a limited length oftime (e.g., during nighttime).

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations arc not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art arc intendedto be included within the scope of the following claims.

What is claimed is:
 1. An automatic drive control system for a bulldozerwhich is capable of automatically driving a bulldozer such that thebulldozer moves back and forth predetermined times between a diggingstart position and a digging end position, the automatic drive controlsystem comprising:(a) digging start detecting means for detecting thatthe bulldozer is in the digging start position; (b) digging enddetecting means for detecting that the bulldozer is in the digging endposition; (c) driving direction detecting means for detecting themomentarily varying driving direction of the bulldozer; and (d) drivecontrolling means for shifting a transmission into a forward gear whenthe digging start detecting means detects that the bulldozer ispresently in the digging start position; shifting the transmission intoa reverse gear when the digging end detecting means detects that thebulldozer is presently in the digging end position; and controlling thebulldozer such that the driving direction detected by the drivingdirection detecting means is made coincident with a target drivingdirection when the bulldozer is moving from the digging start positiontowards the digging end position.
 2. The automatic drive control systemfor a bulldozer as claimed in claim 1, further comprising drivingdirection changing means for changing the driving direction of thebulldozer.
 3. The automatic drive control system for a bulldozer asclaimed in claim 1, further comprising blade controlling means forcontrolling lifting and lowering of the blade such that an actualtractive force exerted on the vehicle body is made coincident with a settarget tractive force while the bulldozer is moving from the diggingstart position towards the digging end position.
 4. The automatic drivecontrol system for a bulldozer as claimed in claim 1, wherein thedigging start detecting means comprises at least one laser projectorinstalled on the ground and a laser beam sensor provided in thebulldozer for receiving a laser beam from the laser projector.
 5. Theautomatic drive control system for a bulldozer as claimed in claim 1,wherein the digging start detecting means comprises at least one laserbeam projecting/receiving device installed on the ground and a reflectorprovided in the bulldozer for reflecting a laser beam directed from thelaser beam projecting/receiving device in the same direction.
 6. Theautomatic drive control system for a bulldozer as claimed in claim 1,wherein the digging start detecting means is a detector which detectsthat the bulldozer has returned to the digging start position, bycounting the number of revolutions of sprockets for actuating crawlerbelts, the count being started immediately after the bulldozer has leftthe digging end position, when the bulldozer moves backwards.
 7. Theautomatic drive control system for a bulldozer as claimed in claim 1,wherein the digging end position is an edge of a cliff from whichremoved soil are to be dropped and the digging end detecting means isfor detecting that the forward end of the bulldozer is on the edge of acliff.
 8. The automatic drive control system for a bulldozer as claimedin claim 7, wherein the digging end detecting means comprises at leastone laser projector installed on the ground and a laser beam sensorprovided in the bulldozer for receiving a laser beam directed from thelaser projector.
 9. The automatic drive control system for a bulldozeras claimed in claim 7, wherein the digging end detecting means comprisesat least one laser beam projecting/receiving device installed on theground and a reflector provided in the bulldozer for reflecting a laserbeam directed from the laser beam projecting/receiving device in thesame direction.
 10. The automatic drive control system for a bulldozeras claimed in claim 7, wherein the digging end detecting means comprisesan ultrasonic sonar provided in the bulldozer for projecting ultrasonicwaves ahead of the vehicle body to detect the presence or absence of theground.
 11. The automatic drive control system for a bulldozer asclaimed in claim 10, wherein the projecting angle of the ultrasonicsonar is adjustable.
 12. The automatic drive control system for abulldozer as claimed in claim 7, wherein the digging end detecting meanscomprises a load detector for detecting a change in load imposed on ablade to estimate the amount of soil present in front of the blade. 13.The automatic drive control system for a bulldozer as claimed in claim 4or 8, wherein the laser projector is rotatable within a vertical planeand the laser beam sensor is disposed such that its longitudinal axis ishorizontally oriented.
 14. The automatic drive control system for abulldozer as claimed in claim 5 or 9, wherein the laser beamprojecting/receiving device is rotatable within a horizontal plane andthe reflector is disposed such that its longitudinal axis is verticallyoriented.
 15. The automatic drive control system for a bulldozer asclaimed in claim 1 or 2, wherein the driving direction detecting meanscomprises an azimuth sensor for detecting a direction, utilizing earthmagnetism.
 16. The automatic drive control system for a bulldozer asclaimed in claim 1 or 2, wherein the driving direction detecting meanscomprises at least two laser beam projecting/receiving devices installedon the ground which are rotatable within a horizontal plane to projectlaser beams synchronously and a reflector which reflects laser beamsdirected from the laser beam projecting/receiving devices in the samedirection and which is provided in the bulldozer such that itslongitudinal axis is vertically oriented.
 17. The automatic drivecontrol system for a bulldozer as claimed in claim 1 or 2, wherein thedriving direction detecting means comprises (i) at least one laserprojector installed on the ground and rotatable within a vertical plane,and (ii) at least two laser beam sensors which are provided in thebulldozer such that their longitudinal axes are horizontally orientedand which receive laser beams directed from the laser projector, andwherein the laser beam sensors detect the relative angle between theplane of a laser beam directed from the laser projector and the vehiclebody, thereby detecting the driving direction of the bulldozer.
 18. Theautomatic drive control system for a bulldozer as claimed in claim 1 or2, wherein the driving direction detecting means detects the drivingdirection of the bulldozer by integrating data from a yaw rate gyroprovided in the bulldozer.
 19. The automatic drive control system for abulldozer as claimed in claim 2, wherein the driving direction changingmeans is a steering system which transmits the power of an engine tofight and left sprockets for actuating crawler belts by means ofclutches and brakes, and the clutches and brakes are independentlyengaged or disengaged prior to a start of dozing operation to change thedriving direction of the bulldozer.
 20. The automatic drive controlsystem for a bulldozer as claimed in claim 2, wherein the drivingdirection changing means tilts the blade laterally during dozingoperation to change the driving direction of the bulldozer.
 21. Theautomatic drive control system for a bulldozer as claimed in claim 1,further comprising remote control means for guiding the bulldozer to adesired digging lane.